Superplastic deformation results from a high sensitivity city of the flow stress to the rate of straining so that large uniform elongations may be obtained. A high strain rate sensitivity may be obtained by temperature cycling a metal about an allotropic transformation temperature or by deforming a very fine grained material at temperatures above 0.5 Tm. This latter method offers more scope for industrial application. The low stress and high ductility found with superplastic alloys enables simple vacuum forming techniques to be employed avoiding the necessity of expensive tool materials. This saving in tooling costs can more than offset the increased material costs of superplastic alloys vis-a-vis conventional alloys.